Plastic bottles, with a neck and an outer thread on the neck, can be closed at the free end of the neck by a closure forming one piece with the neck. A piercer for piercing the closure is conventionally provided on the inside and at the center of a cap screwed onto the neck. When the cap is removed after the piercing of the closure, the liquid in the bottle can then be delivered through the opening formed in the closure by the piercer.
A thread on the bottle neck and/or on the cap in not being of optimum shape, or the piercer in not being of optimum shape can cause the opening made by the piercer to extend at an incline to the longitudinal axis. Additionally, after removal of a partial amount and subsequent screwing-on of the cap, a second opening can be pierced. The inclined and/or multiple piercing results in the liquid flowing out in a direction deviating from the longitudinal axis, possibly at several points, which is troublesome. The pressure exerted on the liquid determines whether the liquid is delivered in larger or smaller drops or in the form of a jet. Furthermore, the size of the opening may change in the course of time if, after removal of a partial amount of the contents of the bottle, the neck is closed again by the cap and the piercer is introduced into the opening again.
Therefore, obtaining the correct dosage of the amount to be removed is difficult.
Additionally, conventional dispensing caps with piercers have flow channels extending in different directions which are difficult to form and require complex molds.